The present invention relates to a variable displacement compressor for use in, for example, a vehicle air conditioner.
In general, variable displacement compressors are used in vehicle air conditioners. One of the compressors of this type is described in, for example, Japanese Second (examined) Patent Publication No. 4-74549.
The disclosed compressor is so-called a wobble plate type variable displacement compressor. The compressor has a compressor casing defining a crank chamber therein. A rotor is disposed in the crank chamber and mounted on a main shaft. A swash plate is attached to the rotor via a hinge mechanism. The main shaft passes through the swash plate. Specifically, a sleeve is attached to the swash plate and receives the main shaft therethrough. A space is formed between an outer periphery of the sleeve and an inner periphery of the swash plate so that an inclination of the swash plate relative to the main shaft can be changed by means of the hinge mechanism.
A wobble plate is attached to the swash plate via a bearing. A plurality of piston rods are coupled to the wobble plate through ball connection. The compressor casing is formed with a plurality of cylinders which are arranged at regular intervals so as to surround the main shaft. Each of the piston rods is coupled through ball connection to corresponding one of pistons disposed in the respective cylinders. In the crank chamber, a guide rod is supported by the compressor casing so as to extend in parallel to the main shaft. The guide rod is sandwiched by an end portion of the wobble plate so that the end portion of the wobble plate is wobbling relative to the guide rod in an axial direction of the main shaft.
Following the rotation of the main shaft, the rotation of the rotor is transmitted to the swash plate so that the wobble plate wobbles to cause the pistons to make reciprocating motions. In this fashion, the compressing operation is carried out. As described above, since the inclination of the swash plate relative to the main shaft is changeable by means of the hinge mechanism, the piston stroke can be changed by controlling the inclination of the swash plate, thereby to change the compression displacement of the compressor.
The foregoing variable displacement compressor has a suction chamber, a discharge chamber, a first communication passage extending from the discharge chamber to the crank chamber, an open/close valve for opening and closing the first communication passage, and a second communication passage or a bleed passage extending from the crank chamber to the suction chamber for constantly allowing discharge gas having flowed into the crank chamber through the first communication passage to escape into the suction chamber.
In the conventional variable displacement compressor of the wobble plate type, the crank chamber and the suction chamber are in constant communication with each other through the bleed passage. Thus, for example, if a liquid refrigerant exists at the low pressure side of a refrigerant circuit while the compressor is stopped for hours, the liquid refrigerant flows into the crank chamber via the suction chamber and through the bleed passage. Particularly, when a temperature in a vehicle compartment is relatively high while a temperature in an engine room where the compressor is installed is relatively low, a large amount of the liquid refrigerant flows into the crank chamber via the suction chamber.
When the compressor is started in this state, a pressure differential is generated across the bleed passage. This is because an open area of the bleed passage becomes insufficient relative to the amount of the liquid refrigerant in the crank chamber. So that, the inclination of the swash plate is held at the minimum compression displacement. As a result, until the liquid refrigerant is sufficiently removed from the crank chamber, the required cooling power can not be obtained.